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As far as I know, when I use Electrum I'm just choosing servers to trust that hold the blockchain.

But in this recently published article I read this about Multibit:

It uses a slightly weaker trust model than Bitcoin-Qt. In SPV mode, with clients like Multibit and Hive, it still scans the blockchain, and what it assumes is whatever blockchain has the majority of miners on it [is correct]. Instead of verifying the entire contents, it just trusts that the majority of miners are honest. It's still peer to peer.

Does this mean that Multibit's SPV implementation is more "P2P" than Electrum? Does it connect to peers (other thin-client users) instead of servers?

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MultiBit connects to (typically) four bitcoinds at random at start up. It then picks the best peer (using ping times, advertised blockchain height and the version of the peer to decide) and uses that as the download peer to get the block headers from.

It is thus using one peer to catch up the blockchain from where it previously knew about.

It listens to all four connections to hear about all the new broadcast transactions and uses this to work out a 'transaction confidence'. If four peers tell it a transaction exists, it has more confidence that the transaction is real.

When it sends a transaction, it sends it via the single download peer and then listens on the other peers to hear that transaction 'echo' back from the network. Once it has heard the transaction it just sent come back via other peer(s) it can be confident that the transaction is 'out in the Bitcoin network'.

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Electrum is not peer-to-peer (P2P). It only connects to electrum-specific servers to broadcast your transactions and to receive transactions. It's very similar to a web-wallet, however you're the one who holds the keys. So the Electrum client signs the transaction with your private key (that you hold), and then sends it to electrum-specific servers that take care of broadcasting it out to other peers.

MultiBit on the other hand does connect to other peers without any proxy server, so it is P2P.

Both Electrum and MultiBit clients download the blockchain headers (not the entire content) so they're considered Simplified Payment Verification (SPV) clients.

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  • wait a sec, are you saying then that MultiBit client is P2P, therefore it's less secure?
    – knocte
    Nov 13, 2013 at 13:46
  • Being P2P doesn't make it less secure. It simply means you connect to several computers instead of one.
    – Luca Matteis
    Nov 13, 2013 at 13:47
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    @knocte to complete what you've said: Electrum client connects to multiple Electrum servers in order to retrieve block headers and find the longest chain. This way it can avoid malicious servers.
    – rdymac
    Nov 13, 2013 at 15:04
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    @knocte it was introduced in 1.9 and some other security improvements github.com/spesmilo/electrum/blob/master/RELEASE-NOTES
    – rdymac
    Nov 13, 2013 at 15:05
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    @knocte you obviously don't know how Bitcoin works, and you've downvoted me nonetheless. Please inform yourself before assuming something is wrong. I don't feel compelled to explain more in details, so I'll just say that: to generate a valid blockchain yourself you'd need more hashing power than the entire network. So no, nor you nor Electrum can fake it!
    – Luca Matteis
    Nov 13, 2013 at 16:53

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